Alkali metals, those in Group 1 of the periodic table, and alloys of alkali metals, are very reactive in their metallic, or neutral, state. The alkali metals and their alloys are very reactive toward air and moisture and may catch fire spontaneously when exposed to these agents. To avoid the inherent hazards associated with their activity, the neutral metal or alloy must often be stored in vacuo or under an inert liquid such as oil in order to protect it from contact with the atmosphere, which may result in oxidation or other reactions. For example, sodium metal is often stored in Nujol oil which must, to avoid unwanted impurities, be removed prior to use in chemical reactions. This places severe restrictions on its shipment and use.
The combination of alkali metals with silica zeolites, such as ZSM-5, has been extensively studied in many laboratories. For example, it was recently shown that pure silica zeolites can absorb up to 12 mole percent cesium from the vapor phase and comparable amounts of the other alkali metals (except lithium). Prior research with alkali metal encapsulation in all-silica zeolites revealed that such a combination reacts exothermically with water to produce hydrogen quantitatively. (See, for example, “Toward Inorganic Electrides”, A. S. Ichimura, J. L. Dye, M. A. Camblor and L. A. Villaescusa, J. Am. Chem. Soc., 124, 1170-1171 (2002) and “Inorganic Electrides Formed by Alkali Metal Addition to Pure Silica Zeolites”, D. P. Wernette, A. S. Ichimura, S. A. Urbin and J. L. Dye, Chem. Mater. 15, 1441-1448, (2003). The concentration of sodium absorbed by the zeolite compositions, however, was too low to be practical. In addition, the reaction was relatively slow with slow sodium diffusion within the limited zeolite pore size.
The use of potassium metal dispersed on silica as a reagent in organic synthesis has been reported by Levy et al., Angew. Chem. Int. Ed. Engl. 20 (1981) p. 1033. Potassium metal was dispersed onto silica gel (CAS Registry No. 7631-86-9: actually colloidal silica, which has no internal surface area) producing an amorphous material. The reactivity of the material was demonstrated with water and benzophenone, as shown below. See also, Russel, et al., Organometallics 2002, 21, 4113-4128, Scheme 3.
It has been reported to disperse sodium on titanium dioxide (TiO2) to readily reduce zinc chloride leading to a highly active zinc powder which inserts into secondary alklyl and benzylic bromides under mild conditions, producing the corresponding zinc reagents in high yield. (See Heinz Stadtmuller, Bjorn Greve, Klaus Lennick, Abdelatif Chair, and Paul Knochel, “Preparation of Secondary Alkyl and Benzylic Zinc Bromides Using Activated Zinc Metal Deposited on Titanium Dioxide” Syntheis, 1995, 69-72.). According to Stadtmuller, it was observed that residual water content in the support has a detrimental effect. For this reason, solid supports like barium, tin, or alumina, as well as silica, could not be used. Commercial TiO2 is almost water free and constitutes the best support for this purpose. Thus the addition of sodium (ca. 8 g/100 g TiO2) to TiO2 (dried at 150° C. for 2 hrs) at 150° C., produces a homogenous, gray powder after 15 min. This powder is not pyrophoric but its exposure to air and moisture results in a slow decomposition (2-3min).
      Na    ⁢          ⟶                        TiO          2                ⁡                  (                                    150              ⁢              °              ⁢                                                          ⁢                              C                .                                      ,                          2              ⁢                                                          ⁢              hrs                                )                      ⁢          Na      /              TiO        2              ⁢      →                  ZnCl        2            ⁡              (                              0            ⁢            °            ⁢                                                  ⁢                          C              .                                ,                      15            ⁢                                                  ⁢            min            ⁢                                                                      ⁢                                                                    ⁢            in            ⁢                                                  ⁢            THF                          )              ⁢      Zn    /          TiO      2      
Stadtmuller's experiment was as follows. A 3-necked 100 mL flask equipped with Ar inlet, a glass stopper, and a septum cap was charged with TiO2 (18 g, 380 mmol) and heated for 2 hr at 150° C. under vacuum (0.1 mmHg). The glass stopper was replaced with a mechanical stirrer, the reaction flask was flushed with Ar and Na (1.50 g, 65 mmol) was added at once. Alternatively, the Na could be added at 25° C. to the dry TiO2. The reaction mixture was vigorously stirred at 150° C. for 15 min and cooled to 0° C. leading to a gray homogenous powder. A solution of dry ZnCl2 (4.57 g, 35.5 mmol) in THF (20 mL) was added with stirring. After 15 min., the activated Zn on TiO2 was ready to use.
Sterling E. Voltz, in “The Catalytic Properties of Supported Sodium and Lithium Catalysts” J. Phys. Chem., 61, 1957, 756-758, investigated the catalytic properties of supported alkali metal catalysts for hydrogen-deuterium exchange and ethylene hydrogenation. Sodium dispersed on dried alumina does not increase the activity of the alumina for hydrogen-deuterium exchange. However, hydriding the sodium-alumina greatly increases the exchange activity, the hydrided catalyst being active even at −195° C. Sodium-silica catalysts are much less active than the corresponding sodium-alumina catalysts. Supported sodium and lithium catalysts are also active for ethylene hydrogenation even below room temperature; in this case, however, hydrogen treatments have relatively minor effects on the activities. The supported alkali metal catalysts are much more active than the bulk hydrides of sodium and lithium for both of these reactions. The major role of the support is probably to increase the effective area of the alkali metal. The results of this study suggest that the mechanisms of activation of hydrogen and ethylene on alkali metal hydrides are similar to those previously postulated for alkaline earth metal hydrides. The activations probably occur at metal sites at metal-metal hydride interfaces. The results obtained with the bulk hydrides suggest that hydrogen activation takes place more readily at lithium sites than at sodium sites, and the reverse situation is likely for ethylene activation.
Voltz's experiment was as follows. The supported sodium and lithium catalysts were prepared by dispersing the molten metal over powdered alumina or silica which had been dried by evacuation at 500° C. for about 16 hours. In a typical preparation (sodium-alumina) the dried alumina and sodium were placed in a high vacuum reactor equipped with a magnetic stirrer. Transfers of materials to the reactor were made in a dry box in dry nitrogen. The reactor was heated lowly under evacuation while the solids were stirred. When the sodium melted, it dispersed over the alumina powder. The reactor was heated to about 150° C. and kept at this temperature (under evacuation and with stirring) for at least one-half hour. Small amounts of gaseous products were given off in some preparations when the molten alkali metal dispersed over the powder. In the preparation of lithium-alumina catalysts, the reactor was heated to about 280° C. because of the higher melting point of lithium (186° C.).
Moreover, Alois Furstner and Gunter Seidel, in “‘High-Surface Sodium’ as a Reducing Agent for TiCl3” Synthesis, 1995, 63-68., disclosed that sodium deposited on inorganic supports such as Al2O3, TiO2, and NaCl (‘high-surface sodium’) is a cheap, readily prepared, nonpyrophoric reducing agent for TiCl3. The low-valent Ti thus obtained, after only 1 hr. reduction time, is well suited for McMurry coupling reactions, particularly of aromatic carbonyl compounds. It exhibits a previously unrivalled template effect for the cyclization of dicarbonyl compounds to (macrocyclic) cycloalkenes and is suitable for the reduction of N-acyl-2-aminobenzophenone derivatives to 2,3-disubstituted indoles.
In this regard, Na/Al2O3 can be conveniently prepared in two different ways as a homogenous grey, nonpyrophoric powder (method A: mixing/grinding of Al2O3 and Na at 180-190° C.; method B: deposition of melting Na on Al2O3 suspended in boiling toluene by means of an Ultra turrax stirrer). With ˜4 mmol Na per g of reagent (10% metal content w/w), the available surface area of the alumina is well exploited without risking any severe overloading.
Furstner's experiment was as follows.
Method A: Na sand (10 g; 1-2 mm) was added in portions during 30 min to predried Al2O3 (100 g) with good mechanical stirring under Ar at 180-190° C. This afforded Na/Al2O3 as a grey-black, air-sensitive but nonpyrophoric powder which can be stored for extended periods of time under Ar at RT without loss of activity. According to Furstner, this simple procedure is less appropriate for the preparation of Na/TiO2 and Na/NaCl for reasons of insufficient mixing.
Method B: To a vigorously stirred suspension of predried Al2O3 (100 g) in boiling Toluene (350 mL) was added Na sand (10 g) over a period of 20 min. Stirring and reflux were continued for another 15 min, the mixture was cooled to RT, filtered under Ar, washed with pentane (ca. 300 mL in several portions) and dried in vacuo. For the preparation of Na/TiO2, a larger volume of toluene (˜800 mL) was required to achieve good agitation. Id.
In addition, U.S. patent application Ser. No. 10/995,327 filed Nov. 24, 2004 and entitled “SILICA GEL COMPOSITIONS CONTAINING ALKALI METALS AND ALKALI METAL ALLOYS” describes silica gel compositions made by interaction of alkali metals or alloys of these metals with silica gel, and is hereby incorporated by reference.
A need exists, therefore, to have alkali metals and their alloys available in a form that may be easily handled without a significant loss in metal reactivity. This invention answers that need.